Office equipment such as printers, scanners, copiers and facsimile machines are in universal use. These types of office equipment often include sheet handling systems to advance sheets of a media such as paper along a media path. Recently, new types of office equipment have been introduced, which combine functions of various machines into a single piece of equipment. These multi-purpose machines include, for example, the "OfficeJet" series of machines marketed by Hewlett-Packard Company, which includes functions of a printer and a facsimile machine.
Many of these multi-function machines use two input media sources, with a drive to pick a sheet of media such as paper from one of the input sources and pass the picked sheet through a shared media path. For example, the machine may include an optical scanner and a printing apparatus, such as a scanning carriage holding an ink-jet print cartridge for example, disposed along a common media path through the machine. One input media source can be for holding documents to be scanned by the optical scanner, and the other media source can be for holding a supply of blank paper for printing. In one mode of operation, document sheets are sequentially fed from the first input source into the shared media path and past the scanning apparatus for optical scanning. In another mode of operation, blank sheets are fed from the second input source into the shared media path and to a printing area for printing by the printing apparatus.
The sheet handling systems of these types of office equipment typically include drive rollers and corresponding pinch or idler rollers, which engage a sheet and drive the sheet along the media path. One system, the large format Design Jet 650C, an ink-jet plotter marketed by Hewlett-Packard Company, the assignee of this application, employs a hard solid rubber drive roller with a hard solid rubber pinch roller. Another system, the Photo Smart (TM) printer marketed by the assignee, employs a grit-surfaced drive roller with a hard rubber pinch roller.
Some sheet handling systems include more than one set of drive/pinch rollers along the media path. An important characteristic of sheet handling systems is the line feed accuracy, which is a measure of the error between the commanded movement of the sheet along the media path and the actual movement resulting from the commanded movement. While ideally there is no error, in practice there will be some error due to various factors including hand-off error. The hand-off error results when the media is engaged by a new set of drive/pinch rollers, or is released by a set of drive/pinch rollers. This invention addresses the problem of hand-off error in sheet handling systems.